Biomass, a renewable energy source, can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuels. Biofuels are derived from biomass and are intended to provide an alternative to petroleum fuels. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into thermal, chemical and biochemical methods. Biomass is a resource that shows promise for advanced biofuels.
Fossil fuels such as petroleum, natural gas and coal are typically formed through the processes of thermochemical conversion (TCC) from biomass buried beneath the ground.
TCC is a chemical reforming process of biomass in a heated and usually pressurized, oxygen deprived enclosure, where long—chain organic compounds break down into short—chain hydrocarbons such as syngas or oil. TCC is a broad term that includes gasification, including the Fischer—Tropsch process, direct liquefaction, hydrothermal liquefaction and pyrolysis.
Pyrolysis is a heating process of dried biomass to directly produce syngas and/or oil. Both gasification and pyrolysis require dried biomass as feedstock and the processes occur in an environment higher than 600° C.
Hydrothermal liquefaction (HTL) is a technology for converting high-moisture waste biomass into energy dense “crude bio-oil” that can be used for direct combustion or refined for transportation grade fuels.
HTL, also called hydrous pyrolysis, is a process for the reduction of complex organic material such as bio—waste or biomass into crude oil and other chemicals.
Hydrothermal Liquefaction (HTL) technique, which involves the application of heat and pressure on the biomass medium, has an advantage that the lipids and other organic components can be efficiently converted while the biomass is in wet condition. During HTL, high moisture biomass is subjected to elevated temperature (250-400° C.) and pressure (up to 225 bars) in order to break down and reform the chemical building blocks into crude bio-oil. HTL of biomass gives only crude bio-oil that needs to be further treated/refined to get finished products. The hydrothermal process breaks down bio macromolecules in the wet biomass and promotes heteroatom removal.
Lipids present in crude bio-oil (CBO) can be extracted by solvent extraction or by physical extraction. However, such techniques may not be able to extract the lipids completely. In order to make biomass an economically viable alternative for bio crude production, the revenues from all their fractions (and not only the lipids) need to be maximized. A high temperature and high pressure is required for thermochemical conversion, in order to processes the whole biomass and produce the crude bio-oil. However, HTL of biomass without catalyst gives about 40% crude bio-oil yield.
WO2010030196 suggests the use of phosphate catalyst for hydrothermal conversion of biomass to crude bio-oil (CBO). Although the products formed from the process are useful, the recovery of the catalyst used in the process is difficult and fresh catalyst needs to be added to each reaction. Also, the phosphate catalyst usually operates at a pH greater than 7, which may have a limiting action on the product range. Metal oxides are also known to provide catalytic activity for conversion of biomass to CBO; these again use basic conditions and there are costs associated with the recovery of the catalyst.
There is, therefore, a need to develop a catalyst assisted hydrothermal process for the conversion of biomass to crude bio-oil (CBO) at high temperature and pressure, which is efficient and cost effective. The present invention discloses a catalyst assisted hydrothermal conversion of biomass to CBO with a high productivity and makes use of catalysts that can be recovered, recycled and reused.